1. Field of the Invention
The present invention relates to an electromechanical harmonic rejection tuner system, and more particularly to such a system to be used in harmonic load-pull setup for the measurement, characterization and testing of RF or microwave devices. Under high power conditions at its input at the fundamental frequency F0, the device under test (hereinafter referred to as “DUT”) generates an output signal that contains the fundamental frequency F0 and the harmonic frequencies of said fundamental frequency F0. RF/Microwave harmonic rejection tuners are electronic devices or mechanical devices which modify in a predictable way the phase of the reflection of harmonics of a given operation frequency F0. The harmonic rejection tuner has the capability of generating high amplitude gamma to the microwave devices at harmonic frequencies. This technique of subjecting DUT input and output to variable high gamma phase with corresponding harmonic source tuner and harmonic load tuner, commonly referred to as “harmonic load pull”, is used to test transistors for amplifier, oscillator or frequency multiplier applications specially at high power, when the non-linear effects of the DUT produces harmonic frequencies.
2. Description of Prior Art
The harmonic load-pull setup is composed of an input generator and its associated amplification (1) connected to input fundamental tuner (2), input harmonic tuner (3), DUT (4), output harmonic tuner (5), output fundamental tuner (6) and the appropriated measurement apparatus (7).
One possible configuration for the harmonic tuner has been proposed in U.S. Pat. No. 6,297,649 issued to Christos TSIRONIS Oct. 2, 2001. These harmonic tuners are comprising a transmission line (9) on which 2 open-stubs (11,12) are sliding on the central conductor (10), which open-stubs are surrounded by a circular side wall (14,14′) and permanently secured on the said side walls through dielectric, low loss washers (13,13′). The open-stubs are then positioned along the transmission line to control the phase of the reflection as indicated by arrows (11″) and (12″). In order to eliminate the residual reflection at the fundamental frequency F0, additional open-stubs (11′,12′) might be added, said additional open-stubs are identical to the first open-stubs (11,12).
The problem remaining with this solution is that when the fundamental frequency F0 changes, the length of each of the open-stubs should be changed to reflect out the desired harmonic frequencies of the new fundamental frequency F0. Therefore, the harmonic rejection load-pull tuner of U.S. Pat. No. 6,297,649 is supplied as a kit with a plurality of open-stubs. Each open-stub is having a length adapted to reflect out an nth order harmonic nF0 of a given frequency F0. In order to solve that problem, U.S. Pat. No. 6,297,649 exposes the possibility of using open-stubs having a variable length to increase Δf. Plungers (100) can be used in order to make the open-stubs lengths (18,19) variables. This will however be accompanied by a decrease in the precision of the measurements, because of the difficulty in precisely adjusting the position of the plunger with the screw. Another drawback of open-stub plungers is that the characteristic impedance of the open-stub (18,19), defined by arrow (101), is different from the characteristic impedance of the plungers (100), defined by arrow (102), since the distances from the open-stubs and the plungers to the grounding walls (14,14′) is necessarily different.